Researchers have found that heavily used shipping lanes pass through crucial whale shark feeding grounds, posing a threat to this endangered species. Research published 15 May in Science of the Total Environment has revealed areas where the sharks are at the highest risk of colliding with large shipping vessels by mapping the locations of whale shark aggregations and overlaying them with information on shipping traffic. The paper is titled “Identifying priority sites for whale shark ship collision management globally”, reports Phys Org.
A growing concern
The world’s merchant fleet has doubled in size in the last 16 years. There are now more than 100,000 ships transporting goods worldwide and this number is expected to grow by as much as 1,200% over the next ~27 years.
Collisions with wildlife—also known as ship strikes, are a growing concern and can be a leading cause of death for large marine animals, with more than 75 species at risk of population-level consequences.
Whale sharks have a declining population and spend almost half their time in surface waters, often in coastal areas that are heavily used by shipping vessels.
Identifying high-risk areas
Although they are mainly solitary creatures, whale sharks regularly come together in search of prey at special sites around the world called constellations. It is especially important to reduce threats to whale sharks inside constellations because the sharks are concentrated in high densities.
Researchers from MARECO, the University of Southampton, the MBA, and the Marine Megafauna Foundation (MMF) drew on the experience of specialists who study whale sharks worldwide to map and gather insights on these constellations.
More than 75 experts responded to a series of survey questions and identified areas where they have encountered the most whale sharks (core habitats) and other places they have been spotted (buffer zones). In total 107 areas were identified in 26 countries. The experts reported observations from over 13 thousand individuals, representing over half of all identified whale sharks.
The team then used information on large ship positions—provided by Global Fishing Watch to understand the density of shipping in each of the constellations.
Whale sharks were most in danger of coming into contact with large vessels off the coast of mainland Ecuador, Isla Mujeres and La Paz in Mexico, Ewing Bank in the northern Gulf of Mexico, Kota Kinabalu and Redang Island in Malaysia, Pintuyan in the Philippines, Musandam in Oman and around the Seychelles and Taiwan.
The researchers identified 39 of these sites where peaks in shipping activity coincided with peak seasonal occurrences of whale sharks, sometimes across several months.
Results showed that some experts involved in the study underestimated the threat posed by large ship collisions within constellation sites due to a lack of direct evidence, such as injuries or witness accounts, which are available for other, sub-lethal threat categories like tourism interactions and small vessel collisions.
Reducing the risk
The research team also looked at how this threat could be mitigated. They simulated vessel movements within the whale shark constellation at Ewing Bank, in the northern Gulf of Mexico.
They found that reducing the speed of vessels passing through the constellation by 75% resulted in a small shipping cost, with an approximate increase in total transit time of 5%, on average, but a potentially high gain for whale sharks as slower ships can better see, and avoid collisions with, the sharks.
Rerouting the ships around core habits had even less of an impact—an approximate 0.5% increase in total transit time (just 2.4 hours per vessel) and a 1.1% increase in total distance traveled, on average.
The researchers say support for these measures requires increased awareness and education of the issue as well as improved data but suggest effective management strategies could pave the way for coexistence between this important species and the shipping industry.
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Source: Phys.Org
